I use a similar configuration for several customers and it works well. However, I only present the OS drive over NFS/VMDK files. For all Exchange Databases, I use guest presented iSCSI LUNs over 1 GBE or 10 GBE and this has been rock-solid and well supported by MS.
It works with storage VMotion, and it always survives storage takeover/giveback (provided that disk timeout settings are applied correctly in the guest Exchange OS). Microsoft does not recommend that Exchange databases be presented as VMDKs over NFS and NetApp SnapDrive makes it so easy to present LUNs to your Guest OS that there is really no good reason to deploy with anything but iSCSI presented to the Native MS iSCSI initiator for your databases.
NetApp Professional Services has deployed hundreds of these configurations and you can find them on the ESRP submissions, so you know you are not out in left field from a support standpoint. We also provide deployment templates (within a service engagement) that can greatly speed your deployment of the software and required database/log LUNs.
